69 lines
3.8 KiB
Markdown
69 lines
3.8 KiB
Markdown
E9H Receiving antennas: radio direction finding (RDF) techniques; Beverage antennas; single- and multiple-turn loops
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- [[E9H01]] (D)
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When constructing a Beverage antenna, which of the following factors should be included in the design to achieve good performance at the desired frequency? #card
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- [[A.]] Its overall length must not exceed 1/4 wavelength
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- [[B.]] It must be mounted more than 1 wavelength above ground
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- [[C.]] It should be configured as a four-sided loop
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- [[D.]] It should be at least one wavelength long
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- [[E9H02]] (A)
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Which is generally true for 160- and 80-meter receiving antennas? #card
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- [[A.]] Atmospheric noise is so high that directivity is much more important than losses
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- [[B.]] They must be erected at least 1/2 wavelength above the ground to attain good directivity
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- [[C.]] Low loss coax transmission line is essential for good performance
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- [[D.]] All these choices are correct
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- [[E9H03]] (D)
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What is receiving directivity factor (RDF)? #card
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- [[A.]] Forward gain compared to the gain in the reverse direction
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- [[B.]] Relative directivity compared to isotropic
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- [[C.]] Relative directivity compared to a dipole
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- [[D.]] Peak antenna gain compared to average gain over the hemisphere around and above the antenna
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- [[E9H04]] (B)
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What is the purpose of placing an electrostatic shield around a small-loop direction-finding antenna? #card
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- [[A.]] It adds capacitive loading, increasing the bandwidth of the antenna
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- [[B.]] It eliminates unbalanced capacitive coupling to the antenna’s surroundings, improving the depth of its nulls
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- [[C.]] It eliminates tracking errors caused by strong out-of-band signals
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- [[D.]] It increases signal strength by providing a better match to the feed line
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- [[E9H05]] (A)
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What challenge is presented by a small wire-loop antenna for direction finding? #card
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- [[A.]] It has a bidirectional null pattern
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- [[B.]] It does not have a clearly defined null
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- [[C.]] It is practical for use only on VHF and higher bands
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- [[D.]] All these choices are correct
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- [[E9H06]] (D)
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What indicates the correct value of terminating resistance for a Beverage antenna? #card
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- [[A.]] Maximum feed point DC resistance at the center of the desired frequency range
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- [[B.]] Minimum low-angle front-to-back ratio at the design frequency
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- [[C.]] Maximum DC current in the terminating resistor
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- [[D.]] Minimum variation in SWR over the desired frequency range
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- [[E9H07]] (B)
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What is the function of a Beverage antenna’s termination resistor? #card
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- [[A.]] Increase the front-to-side ratio
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- [[B.]] Absorb signals from the reverse direction
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- [[C.]] Decrease SWR bandwidth
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- [[D.]] Eliminate harmonic reception
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- [[E9H08]] (A)
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What is the function of a sense antenna? #card
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- [[A.]] It modifies the pattern of a DF antenna to provide a null in only one direction
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- [[B.]] It increases the sensitivity of a DF antenna array
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- [[C.]] It allows DF antennas to receive signals at different vertical angles
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- [[D.]] It provides diversity reception that cancels multipath signals
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- [[E9H09]] (A)
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What type of radiation pattern is created by a single-turn, terminated loop such as a pennant antenna? #card
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- [[A.]] Cardioid
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- [[B.]] Bidirectional
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- [[C.]] Omnidirectional
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- [[D.]] Hyperbolic
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- [[E9H10]] (C)
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How can the output voltage of a multiple-turn receiving loop antenna be increased? #card
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- [[A.]] By reducing the permeability of the loop shield
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- [[B.]] By utilizing high impedance wire for the coupling loop
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- [[C.]] By increasing the number of turns and/or the area enclosed by the loop
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- [[D.]] All these choices are correct
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- [[E9H11]] (B)
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What feature of a cardioid pattern antenna makes it useful for direction-finding antennas? #card
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- [[A.]] A very sharp peak
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- [[B.]] A single null
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- [[C.]] Broadband response
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- [[D.]] High radiation angle
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